Sensitivity time control



Dec; 21, 194a. .E. c. KLUENDER 2,456,952

SENSITIVITY TIME CONTROL Filed May 3, 1946 CONTROL some: 43

SAW TODTH SOURCE Inventor": Edward C. Kluenderm,

H is Attorney.

Patented Dec. 21, 1948 N TED 4, P TENT OFFICE.

Edward C. Kluender, Schenectady, assignor to General Electric' Company,a corporation of New York Applicationli Iayis, 1946, Serial No. 666,897

'3 claims. (01.. 179-171) My invention relates to varying thesensitivity of an electron discharge device amplifiercwith time and moreparticularly to controlling the operationof a remote object detectingsystem in accordance with'thedistan'ce to the remote objects. A a

In one type of remote object detecting system, recurrent pulses of radiofrequency energy are transmitted in thedirectionof remote objectsdesired to be located. Reflected energy pulses, from these objectsarepioked'up by an appropriate radio receiving systemand converted to {aunidirectional voltage 'varying in accord with the intensity of thereceived waves. This voltage, together with time varying-voltagesindicating elapsed time after each transmitted pulse, is applied to acathode ray deviceito pr'oduc'e an indication onthe viewing screenthereof corresponding to the position of each: remote M AY i It is an.object of my invention to provide improved means whereby the sensitivityof the receiving systemof a remote object detecting system is varied in'accordancexwith- ;the time interval-rafter the last transmitted energypulse so that the unidirectional output voltage ofzt'he receiving systemis dependent primarily on. the energy reflecting properties ofthecorresponding reflecting object and not on the distance thereto;

his a further object of my invention'toprovide improved means to'control the. gain of a radio receiver in a manner adaptable to use in. aradio type pulse-echo object detectingsystem.

Another object of .my invention is to provide improved means. to controlthe sensitivity or gain of an electron discharge device'lamplifier aftera predetermined event, whichomeans are simple and reliable inbperation,use a'mimmum number of circuit components, and take-maxi;- mum advantageof the inherent characteristicsof the amplifier circuits. t?

The novel features which I believe to be characteristic of my inventionare set-forth with particularity in the appended claims. 1 My? inventionitself, both as to its organization and method of operation may best beunderstood by reference to the following description taken in connectionwith the accompanying'drawings in which Fig. 1 shows a radio type'pulse-echosystem. incorporating the apparatusof m'yinven- 2 mostadvantageously applied; In the figure, l represents a pulse generatorcapable of generating pulses of radio frequency energy when actuated bycontrol voltage from source 4. Source 4 may, for example, produce 0.5microsecond voltage pulses at a frequency of 1500 pulses per secondacross resistance =42, these pulses having the wave shape shown at 40.These pulses are applied to directional antenna 3, thereby causing adirectional beam of radio frequency energy to be transmitted at theinstant voltage is applied from control source 4. It is the purpose ofT. R. box 2 automatically to prevent entrance of radio frequency energyto unit 5 when generator I is operating. This may; for example, beaccomplished by providinga resonant cavity with a spark gap capable ofbreaking down when pulses are produced by unit I but to pass energy fromantenna 3 to unit-Fat allother times. Radio frequency energy fromgenerator I and radiated by antenna 3 travels from the position ofantenna 3 to a region containing remote ob jectsdesired to be located..These obj'ectsre fleet 'or re-radiate the transmitted energy, there byproducing return waves travelling: inthe 'reverse direction and, afterthe period of time re-' quired to complete the travel, appearing againat antenna 3 from which unit they are applied to unit 5 by T. R. box 2;Units 5, 6, '1, and 30011- stitute a radio receiver, capable ofproducing a unidirectional voltage varying in accordance with theintensity of the reflectedradio frequency energy appearing at antenna 3.This receiver may, for example, be of the superheterodyne type in whichunit- 5 represents the. radio frequency amplifier (if any) the firstdetector, and a first group of intermediate frequency amplifiers (ifany). Two additional stages of intermediate frequency amplification areprovided by the circuits shown generally at 5, these circuits providingadjustment of the receiver gain in a manner to be described in detailhereafter; Unit 1 represents further stages of intermediate frequencyamplification (if any) and the second detector whereas unit 8 representsthe video amplifier portion of the receiver. The unidirectional Voltageproduced by video amplifier 3 is applied to the control electrode ofcathode ray device '9 to vary the intensity of the ray beam of thatdevice in accordance with the reflected radio waves appearing at antenna3. T Source In is arranged to produce a saw tooth current wave aftereach pulse of voltage from control source 4'; This unit might, forexample;

include a square wave voltage generator triggered by voltage of source tand wave shaping amplifiers to change this voltage to the form necessaryto produce a saw tooth current wave in coil I i. This current is appliedto the deflecting coil of cathode ray device 9 to deflect the ray beamfrom the center position in accordance With es agn tu eof this currentttus cans ing this beam to execute successive traverses from the 'centerof the viewing screen to the periphery thereof, each swing taking placeafter a transmitted energy pulse. Inasmuch as the intensity of the raybeam varies in accord with the reflected energy from remote objects-andthe instant of each variation occurs at atime interval after thetransmitted pulse determined by the distance to the corresponding remoteobject, luminous spots appear on the viewing screen corresponding to thevarious remote objects de tected, each spot appearing at a distance fromthe-reenter thereof, determinedbythe di tance between the remote objectand-the detectin equipment andhafiug intensity determine by theintensity oi the, radio echo. The axis alon whichthe electron beam ismovediby aw tooth current from source, It; is varied by m ans ofthevmechanismlshowngenerallyrat t to ome sound with the'direotionof'most intense. radiatiorr from antenna 3. This causes the.-1.umino.us

spots to appear on-thes' viewing screenin add-nectionsfrom the centerthereoi'determined by the direction of the corresponding remote; obiccts'ancliat a: distancedetermined bythe distances the eto, thus producin-on the viewin screen a maul-like indication of the location and radio.re: fl ting: characteristics of remote objects a out the equipmentantenna. 3 and deflectin coil H are1 rotated;

Therintensityoi the received radiant ener y antenna 3 varies inaccordance with'thedistance to the remote objectas well astheadimensionsrand construction thereof: This resu ts from the-fact thatthe attenuationor reduction in. intensity of radio waves let-determinedby the distance; which the t avel- Hence, objects in: closeproximitytothe detecting-equipment produce, stron er a io echoesand hence greatervoltage at" thecontrol electrode of device sz-thanthe same objects iflocated at some distance therefrom. Consequentiy theluminous indicationson the viewing screen .ojf-"devlee 9 corresponding to close objects arerelativelysmuch more intense than the indications of similarobjectsatssomedistancie away. Furthermore; if remoteobjects are to be displayedwithahighxdegreeof brilliance-it is often 'neces.- sary toraise the-'gainof the receiving system to suchahighlevel that extraneous'eehoesdue-to slightly reflecting objectsclose at hand" obscure the-imagescreen; in the area corresponding to the latter objects, therebypreventing: identifioation: of larger objects-located in this area. Thiscondition is shown in Fig; 2' (a) which illus-i trates the appearance..of-v the viewing screen when the gain of the system-. is adjustedatodisplayre! remote objects whileIextraneousroflectionsirom aditrsenumherof sli tly refl tin objects close athand bscure. the-portion of theimagescreen co r sponding t cl se objects. The condition of: therviewingscreen with l minous points indi ea ing: o ly. the actual relativeradioreflecties properties of: the remote obj cts s shown Fig. 2 (b). pI

i Itisthe numosaof: heioircnits: shown eneral y atzfi to: alterh'errelativ s-s sensitivity of," the reeelw objects of like radioreflecting properties to produce like values of voltage at the controlelectrode of device 9. This is accomplished by varying the gain of thesetwo stages of intermediate frequency amplification. The first of thesestages utilizes electron discharge device l3 having its cathodeconnected to ground through bias resistante bland bypass capacitor I5and its anode connected to unidirectional-voltage sou-roe l6 byresistances l1 and I8. The screen electrode of device [3 is connected tothe junction of resistanccs ll and l8 and the radio frequency voltageappearing across this junction bypassed to ground bynondenser l9.-Voltage is applied to the control electrode; of device l3 throughcoupling condenser 20, coil 2!, and bypass capacitor 22. Coil Z I istuned byits-distributed capacitance and the interelectrode capacitancesof device [3 to resonatefiat the frequency of the intermediate frequencyamplifier, thereby causing maximum amplifloetion of si nals of thisfrequency. which migh f example; be .39. me acycles,.per-second.Electron discharge device 23.. is connected in a manner similarsto. devie I 3; deriving its cathode bia voltage iromlresistance-z l; and.capacitor 25, its anode voltage from resistances 26 and 2]" andunidirectional voltage source. 2.8, and havin i screen electrodebypassedto-ground by condenser 2-9 Control electrode volta e is, appliedto this device by means f: coupling: condenser 31L coil 3!.andhypass-condenser'si, c'oil;3.l being tuned by? i s. distributedcapacitance and the inter ele trode capacitancesioi device 23 toresonate atnthe desired-1 intermediate frequency Ample fled. voltagefrom device-231s applied to unit 1 through coupling capacitor'33:Theigainof the amplifier stagesvshowngenerally-.atfiisdetermined bytheunidirectional bias voltage applied to thecontrolelectrodes of devicesl3 and 23 from the network comprising resistances 3A.";S5 and 5i ipotentiometer 31; and unidirectiona1 volta e: source 38. TO1-1 rQVidemaximum-o con, tlfilt l this iashion; devices and 23, are otthevsriab'lcmuor remote eutrofitype in which the ampl cationissreducedasithe negative control electrode-bias voltage is increased;-Manual ad justment o f 1'this-, voltage "is provided by-potenti+ OmGterST'I'; thereby permitting-the operatorof the equipment to controlzthevarying component of beamintensity of cathode ray-device 9 andcause animage ofmaximum usefulness toappear-o'n the image screen thereof.

In additiontothe manual control of the bias voltage at devices 13 and-23: achieved through if variationof potentiometer 31', automatic controlequivalent radioirefl cting properties regardless f? their-distance fromth pulswechosystem.

operation: oi:.-t.h.e. circuit of Fig: 1- to on duce the varyingdegree.of sensitivity" of the resistance 35, condenser 32,and the' currentpaththrough inductance-3l,*-the control electrode; cathode space patho'fdevice 23;"andresistance 24; the latter current path being in'shuntwith condensers 39 and 32 immediately begin to charg'ef the charge beingin direction" tending to'make point 4| relatively more positive andtaking place at a time constant determined "primarily byresistance 35;The'actual positivevoltage at this point, however, is limited by thecontrol electrodecathode space path current of device '23 which beginsto flow as soon as condenser sz ce'mmences to charge. Inasmuch asthiscurrent does not charge condenser 32, itproduces no voltage thereacrossand correspondingly reduces the positive potential of point 4l-, belowthepotentialr that would exist in the absence ofzdevice'23.

Inasmuch as the charge oncondenser 32 cannot change when the voltage ofwave 40 disappears, the potential of point 4! remains constant at thattime. However, charging of condensers 3-9 and 32 immediately begins, thetime constant v of this charge :being determined principally by thevalue of resistance 35.' Resistor 42 has a low value as compared to theresistor 35. Due to the large capacity of thecapacitor 39 as comparedwith the capacitor 32, and the relative discharge condition of 32resulting from its discharge by the device 23, the capacitor 39 quicklycharges 32 until it has substantially the same negative potential. Aftertheir voltages become equal. they then both discharge through theresistors 36, 31 and 42. This discharge continues until capacitors 39and 32 each reach a predetermined potential as determined by the valueof resistor 31.

The above-described negative voltage at point 4| appears very soon afterthe pulse of Wave 40 disappears since the time constant of the circuitsinvolved is relatively short. The resultant charge on condensers 32 and39, however, leaks off through the relatively long time constant circuitincluding resistance 36 and potentiometer 31. This relatively slow decayof negative voltage slowly increases the gain of amplifier 23 and thusrestores the sensitivity of the receiver after the transmitted energypulse at a rate commensurate with the decreased intensity of echo pulsesat antenna 3.

During the time of each transmitted pulse, when the control electrode ofdevice 23 is positive with respect to the cathode, amplifier 6 isinoperative. However, this does not influence performance of thepulse-echo system since breakdown of the spark gap in T. R. box 2prevents radio energy from antenna 3 from entering the receiver duringthis period. Similarly, the short period of time after each pulse duringwhich point 4| has a positive voltage does not influence systemoperation because T. R. box 2 does not permit radio energy to pass fromantenna 3 to the receiver for a corresponding time after each a pulse.

The above description has been made with reference to condenser 32 anddevice 23 only. The current path through resistance 34 and condenser 22,together with the current'path through inductance 2| and the controlelectro-cathode space path of device 13, also influences this action. Ineffect these current paths are in parallel with the current paths due tocapacitor 32 and device 2a and, whilethey' alter the relativedistribution of voltage after the positive pulses of wave-40 and thetime constant of gain restoration ofthe receiver, they do notalter thebasic operation of In a" particular embodiment of theabove -describedcircuit which has been found to operate satisfactorily in practice, thefollowing-circuit conditions existed:

i f b microsecond P lses of 50 vol s jat the rate of 1200 pulses persecond. I, Capacitor 39-001 microfarad Capacitors I5, 22, 25 and 32-0001microfarad";

Resistances i4 and 24-120 ohms Resistances 34 and 35-180 ohms Condensers20 and 300.005 microfarad Resistance 363000 ohms Source 38--210 voltsPotentiometer 31210,000 ohms Devices l3 and 23-Type 6AK5 It hasheretofore been considered necessaryin .gaincontrol devices of. the typeherein described to apply a negative voltage pulse to the controlelectrodes of the electron discharge devicesdesired to be renderedinsensitive. .This has required the use of special equipment to generatethese pulses in a satisfactorymanner, suchequipment generally requiringmultivibrators, gas

tubes, rectifiers, amplifiers, additional transformers and the like.This not only increases the expense of the equipment but also decreasesthe reliability and adds to the complexity thereof. I have discoveredthat a method contrary to that of the prior art produces superior andunanticipated results, probably as a result of the theory outlinedherein. Thus by taking advantage of the inherent characteristics of thecircuits, I am enabled to produce a negative bias voltage varying inaccordance with the desired gain control without the disadvantages ofthe prior art circuits.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from my invention in itsbroader aspects. In particular, this system is applicable to radioreceivers and electron discharge device amplifiers other than thepulse-echo equipment specifically described herein. Furthermore, theprinciples of this invention may be applied to pulse-echo equipmentsutilizing waves other than radio waves and displaying the location ofremote objects in a manner different from that described herein. Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a radio detecting apparatus of the type wherein radio energypulses are successively transmitted and the corresponding reflectedenergy received to determine the location of remote objects, an electrondischarge device having a cathode, control electrode, and anode, saiddevice being capable of reducing the sensitivity of said system as saidcontrol electrode has increased negative potential relative to saidcathode, pulse generating means to produce a voltage wave havingpositive pulses at the instants of said transmitted pulses, means toimpress said positive pulses upon a time constant network comprisingfirst and second capacitors in series, means connecting the controlelectrode-to-cathode path of said device across said second capacitor,said oncogene P? 38 math i'bcing rendered ,conductive ibyisaid pulse :tomy athe woltage Iflletween 5a. :eontrol electrode sand ea iprovide 9alow impedance across :said "second nathodesa'sourcecofpositivemoltage;rpu1ses,.means scapacitoriduring each; pulse;saidznetworkmaving zto-impzess said zpulses upon a -;-time .constantmetto. low '..time r constant zrela'tive 1to:the {pulse 1period, "work:cnznprising afil'st .and second capacitors, 1 in said first capacitorbeing charged rapidly by said as .series, .nneans {connecting the"control grid-(t0- apiilseswandzdischargingrrapidlyzintotsaid asecondcathode xpace :path iof said device :across said mapacitor :at Lthetermination of, :each spulse, -second capacitor,;-saidpathbeingi-rendered-conithereby :to rreducethe rsensitivitykofisaid:syst'em, fluctiveby-said puiseszto shunnsaidrsecond capacand means fordischarging said mapacitors'rat :2, itor-iforithedurationaof.saidpulsesg said network i-predetermined rate .to.restore. said sensitivity,ahavingazshonttimeconstant rrelative tozthespulse '2. In combination, anelectromdischarge device period,-said first.capacitor:Joeing:chargediforndurahaving cathode, anode,and'controLelectrodes a, ation of 1said-.pu1ses and scharging :s-aid,second pulse generating source, two icapacitors in series aeapeitvri-rapidlyiupon terminationof each pulse, connection acrosssa'i'disource, means connecting fi er-8103' tO-I'Bduce-the ampl fic flnof d device, the cathodeecontrol electrode space pathof said 15andsmeans-foradischarg n a d cfllp s 1704116- device across one ofsaidcapacitorsso 'that;sai'd z storxe the amplification \ofisaid device at:a {precontrol electrode "becomes positive :with respectdetermined-rate. to-said cathode when a positive pulse ;is amilied VZEDWARD CJKLUENDER. from said source, ,meansiorapplymg anegatmepotential to said vcontrol -,1ec-tr0de at 'the'.ter---;20 REFERENCESCITED mination of said pu1se,thus causing said control mifinowmgirefermces sarerof record zt ilentrode -to have apnegativepotential relative to fil of :sai'd ncathode, and means for dischargingsaid mapae'itors to remove :said'negative potential at UNITEDSTATESPATENTS a rpre'determined rate. 26 Number Name Date 131Asensitivity control circuit :compris'ing, in -2;374,20.4 Hoover April24, 1945 -conibination, an amp1ifier in'c1uding aneleritron 2375283Cloud I'May 8, 1945 sfiisohargeideviceihaving 'amplificatiomdetemiined2,427,523 Delberg -Sept. 16, 31947

